[PATCH v3 17/35] x86/bugs: Restructure l1tf mitigation

David Kaplan
2025-01-08T20:25:49Z

Restructure l1tf to use select/apply functions to create consistent
vulnerability handling.

Define new AUTO mitigation for l1tf.

Signed-off-by: David Kaplan <david.kaplan@amd.com>
---
arch/x86/include/asm/processor.h | 1 +
arch/x86/kernel/cpu/bugs.c | 27 +++++++++++++++++++++------
arch/x86/kvm/vmx/vmx.c | 2 ++
3 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 90278d0c071b..57760b0d553e 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -746,6 +746,7 @@ void store_cpu_caps(struct cpuinfo_x86 *info);

enum l1tf_mitigations {
L1TF_MITIGATION_OFF,
+ L1TF_MITIGATION_AUTO,
L1TF_MITIGATION_FLUSH_NOWARN,
L1TF_MITIGATION_FLUSH,
L1TF_MITIGATION_FLUSH_NOSMT,
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index b07726a8dd3b..08ac515df888 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -67,6 +67,7 @@ static void __init spectre_v2_user_apply_mitigation(void);
static void __init ssb_select_mitigation(void);
static void __init ssb_apply_mitigation(void);
static void __init l1tf_select_mitigation(void);
+static void __init l1tf_apply_mitigation(void);
static void __init mds_select_mitigation(void);
static void __init mds_update_mitigation(void);
static void __init mds_apply_mitigation(void);
@@ -225,6 +226,7 @@ void __init cpu_select_mitigations(void)
retbleed_apply_mitigation();
spectre_v2_user_apply_mitigation();
ssb_apply_mitigation();
+ l1tf_apply_mitigation();
mds_apply_mitigation();
taa_apply_mitigation();
mmio_apply_mitigation();
@@ -2535,7 +2537,7 @@ EXPORT_SYMBOL_GPL(itlb_multihit_kvm_mitigation);

/* Default mitigation for L1TF-affected CPUs */
enum l1tf_mitigations l1tf_mitigation __ro_after_init =
- IS_ENABLED(CONFIG_MITIGATION_L1TF) ? L1TF_MITIGATION_FLUSH : L1TF_MITIGATION_OFF;
+ IS_ENABLED(CONFIG_MITIGATION_L1TF) ? L1TF_MITIGATION_AUTO : L1TF_MITIGATION_OFF;
#if IS_ENABLED(CONFIG_KVM_INTEL)
EXPORT_SYMBOL_GPL(l1tf_mitigation);
#endif
@@ -2582,23 +2584,36 @@ static void override_cache_bits(struct cpuinfo_x86 *c)
}

static void __init l1tf_select_mitigation(void)
+{
+ if (!boot_cpu_has_bug(X86_BUG_L1TF) || cpu_mitigations_off()) {
+ l1tf_mitigation = L1TF_MITIGATION_OFF;
+ return;
+ }
+
+ if (l1tf_mitigation == L1TF_MITIGATION_AUTO) {
+ if (cpu_mitigations_auto_nosmt())
+ l1tf_mitigation = L1TF_MITIGATION_FLUSH_NOSMT;
+ else
+ l1tf_mitigation = L1TF_MITIGATION_FLUSH;
+ }
+
+}
+
+static void __init l1tf_apply_mitigation(void)
{
u64 half_pa;

if (!boot_cpu_has_bug(X86_BUG_L1TF))
return;

- if (cpu_mitigations_off())
- l1tf_mitigation = L1TF_MITIGATION_OFF;
- else if (cpu_mitigations_auto_nosmt())
- l1tf_mitigation = L1TF_MITIGATION_FLUSH_NOSMT;
-
override_cache_bits(&boot_cpu_data);

switch (l1tf_mitigation) {
case L1TF_MITIGATION_OFF:
+ return;
case L1TF_MITIGATION_FLUSH_NOWARN:
case L1TF_MITIGATION_FLUSH:
+ case L1TF_MITIGATION_AUTO:
break;
case L1TF_MITIGATION_FLUSH_NOSMT:
case L1TF_MITIGATION_FULL:
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 893366e53732..99bdb9341be0 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -273,6 +273,7 @@ static int vmx_setup_l1d_flush(enum vmx_l1d_flush_state l1tf)
case L1TF_MITIGATION_OFF:
l1tf = VMENTER_L1D_FLUSH_NEVER;
break;
+ case L1TF_MITIGATION_AUTO:
case L1TF_MITIGATION_FLUSH_NOWARN:
case L1TF_MITIGATION_FLUSH:
case L1TF_MITIGATION_FLUSH_NOSMT:
@@ -7643,6 +7644,7 @@ int vmx_vm_init(struct kvm *kvm)
case L1TF_MITIGATION_FLUSH_NOWARN:
/* 'I explicitly don't care' is set */
break;
+ case L1TF_MITIGATION_AUTO:
case L1TF_MITIGATION_FLUSH:
case L1TF_MITIGATION_FLUSH_NOSMT:
case L1TF_MITIGATION_FULL:
--
2.34.1